The global adaptive convergence of subterranean mammals currently involves 3 orders: rodents, insectivores and marsupials. These include 11 families, 50 genera, and several hundreds of species. This global evolutionary process followed the stepwise climatic cooling and drought followed by biotic extinction in the transition from the middle Eocene to the early Oligocene, a period of 10 million years (35-45 Ma = million years ago), of profound change in earth geology, climate and biota. The earth changed from the Mesozoic "hot house" to the Neogene (Miocene to Present) "cold house", ie from a warm, equable, mostly subtropical world that persisted from the Mesozoic to the beginning of the present glaciated world. The ecological theater of open country biotas, that opened up progressively in the Cenozoic following the Eocene-Oligocene transition, was associated with increasing aridity, colder climate, and terrestrialism. This climatic change set the stage for a rapid evolutionary play of recurrent adaptive radiations of unrelated mammals on all continents into the subterranean ecotope. The subterranean ecotope is relatively simple, stable, specialised, low or medium in productivity, predictable and discontinuous. Its major evolutionary determinants are specialization, competition and isolation. This ecotope involves the herbivorous (rodents) and insectivorous (insectivores and marsupials) niches. All subterranean mammals share molecular and organismal convergent adaptations to their common unique ecology. By contrast, they display divergent adaptations to their separated niches of herbivory and insectivory and to their different phylogenies. The remarkable adaptive evolution of subterranean mammals involves adaptive structural and functional progression and regression. It is one of the most dramatic examples of global convergent evolution due to underground ecological constraints, at both the molecular and organismal levels of evolutionary theory.
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